Microbiome ‘social network’ revealed by gene swaps

To understand how microorganisms and their genes traverse the globe, Ilana Brito maxed out her own credit card, bought dewars of liquid nitrogen to preserve her samples, and flew to Fiji. Brito, who is now a microbiologist at Cornell University in Ithaca, New York, and her colleagues sampled microbes from the hands, saliva and faeces of people in five villages to map the spread of microbial genes across the villagers’ social networks.

The long-awaited results of this project are published this week in Nature1. The study suggests that day-to-day interactions between people can affect the transfer of genes in the human microbiome — between and across species of microorganisms that thrive in the body. This ongoing exchange of genes could help to reveal how an individual’s microbiome influences his chance of disease, and why some populations seem to be more susceptible to certain disorders.

Brito and her colleagues compared the microbiomes of 172 Fijians with those of 81 North Americans, surveying thousands of mobile genes for evidence of transfer across populations. Bacteria readily swap genetic information with their neighbours, even across species — a process that can make an organism more or less virulent, or confer resistance to a particular antibiotic.

The scientists also sequenced individual cells to see the entire set of genes within, and to identify which elements on a given gene are mobile. And the team analysed genetic material from the cheek swabs, saliva and faecal samples collected from each village in Fiji.

The result is a massive trove of genetic data — the first sequencing effort of this scale to document a developing-world microbiome.

Focusing on a relatively isolated island population had several advantages. “These people tend to stick around in the same …

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